1. Field of the Invention
The present invention relates to a travelling-wave tube amplifier suitable for amplifying microwaves, more particularly to a travelling-wave tube amplifier using a multi-stage collector type travelling-wave tube.
2. Description of the Related Art
Digital communication technology has been spread widely in the recent telecommunications field instead of analog communication technology. In the digital communication system, usually one amplifier simultaneously amplifies a plurality of signal waves (so called, multi-carrier) whose frequencies are slightly different from each other. Such multi-carrier amplification is a popular technique for digital communications, and requires many amplifiers for high frequency such as those frequencies in a microwave band. A travelling-wave tube amplifier is suitable for such a high frequency amplifier. The typical travelling-wave tube amplifier comprises a travelling-wave tube having an electron gun, a high frequency circuit, collector electrodes, and a power source for driving the travelling-wave tube.
Generally, the travelling-wave tube amplifier employs a multi-stage collector type travelling-wave tube. In such the multi-stage collector type travelling-wave tube, multiple collector electrodes are prepared in order to sequentially reduce potentials at each collector electrode. As a result, the travelling-wave amplifier realizes improved energy conversion.
In the high frequency circuit, an electron beam emitted from the electron gun interacts with a high frequency signal. Energy of the electron beam amplifies the high frequency signal. Then the electron beam goes toward the collector electrodes. Each of the electrons in the electron beam is captured by the collector electrodes. The relationship between an electron and collector electrode that capture the electron depends on energy condition of each electron. Since the electron beam is subjected to velocity modulation in the high frequency circuit, a collector current includes a direct current component and a modulated current component. The modulated current component returns to the power source via collector leads. The modulated current component in the collector current is an unnecessary component for the power source. In other words, the power source regards the modulated current component as ripple.
In a case where the travelling-wave tube amplifier amplifies a plurality of signal waves for the multi-carrier amplification, distortion waves caused by non-linearity of the travelling-wave tube amplifier appear. Intermodulation waves also appear. Frequency components in the intermodulation waves correspond to a frequency difference between two signal waves of the plurality of signal waves. Since a given frequency interval in the plurality of signal waves to be amplified is in the range from several kHz to tens of MHz in accordance with the applied communication system, the intermodulation waves have the frequency component in the range from several kHz to tens of MHz. Accordingly, the modulated current component in the collector current is also in the range from several kHz to tens of MHz.
The modulated current component returns to the power source. When the frequency component of the intermodulation waves is synchronous with an unstable zone of the power source, irregular phenomenon such as oscillation occur. Such unstable phenomenon in the power source prevent regular high frequency amplification, that is, unstable amplification. Moreover, the travelling-wave tube amplifier may be damaged if an irregular voltage is applied thereto. Accordingly, the unstable phenomenon in the power source disturb regular functions of the travelling-wave tube amplifier.
In other technical fields, various techniques regarding to restraining unnecessary components have been proposed. For example, Unexamined Japanese Patent Application KOKAI Publication No. H8-46808 discloses a technique for canceling unnecessary pulses in a high voltage generator circuit for a CRT (Cathode Ray Tube) display. Unexamined Japanese Patent Application KOKAI Publication No. H4-32003 discloses a noise reduction technique for a multi-track tape recorder, which reduces low frequency (equal to or lower than 360 Hz) noises plunged into wiring near the recorder""s head. Unexamined Japanese Patent Application KOKAI Publication No. S60-12590 discloses a technique for offsetting crosstalk between channels in a magnetic recording/reproducing apparatus. The disclosures of the above Japanese Patent Applications are incorporated herein by reference in their entirety.
The techniques disclosed in Unexamined Japanese Patent Application KOKAI Publication Nos. H8-46808, H4-32003 and S60-125902 belong to a technical field that is inconsistent with the technical field for the present invention, travelling-wave tube amplifiers.
It is an object of the present invention to restrain unnecessary components which appear at every section from a travelling-wave tube to a power source for driving it.
It is another object of the present invention to enable a travelling-wave tube amplifier to be driven stably.
It is a further object of the present invention to provide excellent frequency characteristics with a travelling-wave tube amplifier.
To accomplish the above objects, a travelling-wave tube amplifier according to a first aspect of the present invention is a travelling-wave tube amplifier comprising:
a travelling-wave tube causing interaction between an electron beam and an input high frequency signal to amplify the high frequency signal and cause a velocity modulation of the electron beam, and outputting an amplified high frequency signal;
a plurality of collector electrodes capturing the electron beam, and being subjected to the velocity modulation of the electron beam;
a plurality of collector leads electrically connecting each of said collector electrodes to a power source; and
at least one magnetic core comprising a respective through hole,
wherein any two of the plurality of said collector leads pass through said through hole in one of said magnetic cores, and
respective currents flowing through said two collector leads passing through said through hole in said magnetic core generate corresponding magnetic fluxes in said magnetic core with directions which are reversed from each other.
According to this structure, the magnetic fluxes, which are generated in the magnetic core and whose directions are reversed from each other, cause induction currents to flow through the two collector leads through the though hole in the magnetic core. The directions of those induction currents are reversed from the directions of the currents which originally flow through the two collector leads through the through hole in the magnetic core. Therefore, those induction currents restrain unnecessary components in the whole structure from the travelling-wave tube to the power source caused by the electron beam which was subjected to velocity modulation. As a result, the travelling-wave tube amplifier functions stably with excellent frequency characteristics.
In a first preferred embodiment for the travelling-wave tube amplifier according to the first aspect of the present invention, the power source applies a first voltage to an emission source of the electron beam, applies a voltage higher than the first voltage to one of said collector electrodes which is the furthest from said emission source of the electron beam, and sequentially applies higher voltages to respective ones of said collector electrodes closer to the emission source of the electron beam than said one which is the farthest. This structure has advantage that electrons in the electron beam, whose energy conditions are different from each other because the electron beam is subjected to velocity modulation, are fully captured in accordance with the energy conditions.
In a second preferred embodiment for the travelling-wave tube amplifier according to the first aspect of the present invention, two of the plurality of said collector leads pass through said magnetic core in opposite directions. This structure has the advantage that the directions of the magnetic fluxes generated in the magnetic core by the two collector leads are reversed from each other, because the directions of the currents flowing through the two collector leads through the through hole in the magnetic core are reversed from each other. This structure has advantage that the directions of the magnetic fluxes generated in the magnetic core by the two collector leads are reversed from each other, because the directions of the currents flowing through the two collector leads through the through hole in the magnetic core are reversed from each other.
In a third preferred embodiment for the travelling-wave tube amplifier according to the first aspect of the present invention, two of the plurality of the collector leads pass through the through hole in the magnetic core a predetermined number of times. This structure has advantage that the range of frequencies in unnecessary components is adjustable in accordance with how many times the collector leads go through the through hole. Thus, the unnecessary components can be restrained more effectively.
In a fourth preferred embodiment for the travelling-wave tube amplifier according to the first aspect of the present invention, the magnetic core has a ring-like cross section. This structure has advantage that unnecessary components can be restrained more effectively because the magnetic fluxes are generated efficiently.
In a fifth preferred embodiment for the travelling-wave tube amplifier according to the first aspect of the present invention, the magnetic core includes a ferrite member. This structure has advantage that the magnetic fluxes are generated in the magnetic core without failure because high frequency losses are reduced.
A travelling-wave tube amplifier according to a second aspect of the present invention is a travelling-wave tube amplifier comprising:
an electron gun emitting an electron beam;
a high frequency circuit causing interaction between the electron beam and an input high frequency signal to amplify the high frequency signal, subjecting the electron beam to a velocity modulation, and outputting an amplified high frequency signal;
a collector section including first and second collector electrodes for capturing the electron beam subjected to said velocity modulation;
first and second collector leads, each lead respectively having one end thereof being electrically connected with any one of said first and second collector electrodes while the other end thereof being electrically connected to a power source; and
at least one magnetic core comprising a respective through hole,
wherein each of said first and second collector leads passes through said through hole in one of said magnetic cores, and
respective currents flowing through said first and second collector leads generate corresponding magnetic fluxes in said magnetic core with directions which are reversed from each other.
According to this structure, the magnetic fluxes, which are generated in the magnetic core and whose directions are reversed from each other, cause induction currents to flow through the two collector leads through the though hole in the magnetic core. The directions of those induction currents are reversed from the directions of the currents which originally flow through the two collector leads through the through hole in the magnetic core. Therefore, those induction currents restrain unnecessary components in the whole structure from the travelling-wave tube to the power source caused by the electron beam which was subjected to velocity modulation. As a result, the travelling-wave tube amplifier functions stably with excellent frequency characteristics.
In a first preferred embodiment for the travelling-wave tube amplifier according to the second aspect of the present invention, the power source applies a first voltage to said electron gun, applies a voltage higher than the first voltage to a furthest one of said collector electrodes which is further from said electron gun than any other collector electrode, and sequentially applies higher voltages to respective ones of said collector electrodes closer to said electron gun than said furthest one. This structure has advantage that electrons in the electron beam, whose energy conditions are different from each other because the electron beam is subjected to velocity modulation, are fully captured in accordance with the energy conditions.
In a second preferred embodiment for the travelling-wave tube amplifier according to the second aspect of the present invention, the first and second collector leads pass through said magnetic core in opposite directions. This structure has advantage that the directions of the magnetic fluxes generated in the magnetic core by the two collector leads are reversed from each other, because the directions of the currents flowing through the two collector leads through the through hole in the magnetic core are reversed from each other.
In a third embodiment for the travelling-wave tube amplifier according to the second aspect of the present invention, each of said first and second collector leads pass through said through hole in said magnetic core a predetermined number of times. This structure has the advantage that the range of frequencies in unnecessary components is adjustable in accordance with how many times the collector leads go through the through hole, thus, the unnecessary components can be restrained more effectively.
A travelling-wave tube amplifier according to a third aspect of the present invention is a travelling-wave tube amplifier comprising:
an electron gun emitting an electron beam;
a high frequency circuit causing interaction between the electron beam and an input high frequency signal to amplify the high frequency signal, and outputting an amplified high frequency signal;
a collector section including N (positive integer equal to or greater than 2) collector electrodes for capturing the electron beam to which velocity modulation is subjected in said high frequency circuit;
N collector leads, each lead respectively having one end thereof being electrically connected to any one of said N collector electrodes, and the other end thereof being electrically connected to a power source; and
Nxc3x97(Nxe2x88x921)/2 magnetic cores, each of said cores comprising a respective through hole,
wherein selected two of said N collector leads pass through a one of said through holes in said magnetic cores,
respective currents flowing through said selected two of said collector leads generate corresponding magnetic fluxes in said magnetic cores with directions which are reversed from each other, and
combinations of said selected two of said collector leads passing through said through holes in said Nxc3x97(Nxe2x88x921)/2 magnetic cores are different from each other.
According to this structure, the magnetic fluxes, which are generated in the magnetic core and whose directions are reversed from each other, cause induction currents to flow through the two collector leads through the though hole in the magnetic core. The directions of those induction currents are reversed from the directions of the currents which originally flow through the two collector leads through the through hole in the magnetic core. Therefore, those induction currents restrain unnecessary components in the whole structure from the travelling-wave tube to the power source caused by the electron beam which was subjected to velocity modulation. As a result, the travelling-wave tube amplifier functions stably with excellent frequency characteristics. Moreover, since the suitable number of magnetic cores corresponding to the collector electrodes and collector leads are given, the unnecessary components are restrained without failure because the number of the magnetic cores are satisfied for each of the collector leads.
In a first preferred embodiment for the travelling-wave tube amplifier according to the third aspect of the present invention, the power source applies a first voltage to said electron gun, applies a voltage higher than the first voltage to a furthest one of said collector electrodes which is further from said electron gun than any other collector electrode, and sequentially applies higher voltages to respective ones of said collector electrodes closer to said electron gun than said furthest one. This structure has advantage that electrons in the electron beam, whose energy conditions are different from each other because the electron beam is subjected to velocity modulation, are fully captured in accordance with the energy conditions.
In a second preferred embodiment for the travelling-wave tube amplifier according to the third aspect of the present invention, the selected two of said N collector leads pass through said magnetic core in opposite directions. This structure has advantage that the directions of the magnetic fluxes generated in the magnetic core by the two collector leads are reversed from each other, because the directions of the currents flowing through the two collector leads through the through hole in the magnetic core are reversed from each other.
In a third preferred embodiment for the travelling-wave tube amplifier according to the third aspect of the present invention, the selected two of said N collector leads pass through said one of said through holes in said magnetic cores a predetermined number of times. This structure has advantage that the range of frequencies in unnecessary components is adjustable in accordance with how many times the collector leads go through the through hole, thus, the unnecessary components can be restrained more effectively.
A magnetic core assembly according to a fourth aspect of the present invention is a magnetic core comprising:
a plurality of collector leads, each lead respectively having one end thereof being connected to a plurality of collector electrodes to which different voltages are applied and the other end thereof being connected to a power source; and
a magnetic core comprising a through hole through which any two of the plurality of said collector leads pass,
respective currents flowing through said two collector leads generate corresponding magnetic fluxes in said magnetic core with directions which are reversed from each other.
According to this structure, the magnetic fluxes, which are generated in the magnetic core and whose directions are reversed from each other, cause induction currents to flow through the two collector leads through the though hole in the magnetic core. The directions of those induction currents are reversed from the directions of the currents which originally flow through the two collector leads through the through hole in the magnetic core. Therefore, those induction currents restrain unnecessary components included in the two collector leads.